1. Field of the Invention
The present invention relates to a liquid crystal composition, and more particularly to a liquid crystal composition suitable for liquid crystal display devices of the twisted nematic mode in which a multiplex drive scheme is employed.
2. Description of the Prior Art
Recently, the enlargement of the information content of a display device has been needed in the field of liquid crystal display devices. Liquid crystal display devices of the matrix display type are being supplied more and more because they are more appropriate for the enlargement of the information content than liquid crystal display devices of the segment display scheme which have previously been used. The increase in the number N of multiplexed lines of the multiplex drive in the matrix display scheme is also demanded in order to develop the diversification of the display further. In the matrix display, the multiplexity (N) in the multiplex driving is desired to be increased to 32, 64, or more so as to further diversify the information content.
The drive of a liquid-crystal of X-Y matrix type by the optimized amplitude-selecting method of the multiplexity and the ratio .alpha. of the effective voltage Vrms (on) in the selected picture-element to the effective voltage Vrms (off) in the non-selected picture-element is given as well known by the following formula: ##EQU1## When the N is .infin. in the formula, the .alpha. value becomes 1. As apparent from this formula, the ratio of the Vrms (off) to the Vrms (on) should be smaller as the multiplexity N increases. Accordingly, the matrix type liquid-crystal display devices of a high information content require a liquid-crystal material of sharp threshold characteristics, i.e., of superior contrast ratio provided by the small voltage ratio. The threshold characteristics of the conventional liquid-crystal material were not good enough that problems such as a low display contrast, narrow effective viewing-angle range, etc. were caused under the matrix driving operation of the liquid-crystal panel wherein the N became a large value of 32 or higher.